Method and apparatus of transmit power control in wireless local area network

ABSTRACT

A method and apparatus of controlling a transmit power in a wireless local area network is provided. A wireless device operated in a TV White Space transmits a white space map indicating a list of available channels, and transmits an extended power constraint indicating a plurality of transmission channels and a plurality of maximum transmit powers, wherein the plurality of transmission channels are selected among the list of available channels and each of the plurality of maximum transmit powers corresponds to a maximum transmit power for each of the plurality of transmission channels. Interference can be mitigated between wireless devices operated in the TV White Space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of U.S. Provisionalapplications 61/300,805 filed on Feb. 2, 2010, 61/321,508 filed on Apr.7, 2010, Korean Patent Applications No. 10-2010-0066804 filed on Jul.12, 2010, and Korean Patent Applications No. 10-2010-0104910 filed onOct. 26, 2010, all of which are incorporated by reference in theirentirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for controlling a transmit powerin a wireless local area network.

2. Related Art

With recent development of information and communications technology,various wireless communications technology has been developed. Amongthem, a wireless local area network (WLAN) is technology that allowsportable user equipment such as a personal digital assistant (PDA), alaptop computer, a portable multimedia player (PMP), etc. in a home, anenterprise or a certain service providing zone to have wireless accessto high-speed Internet on the basis of radio frequency technology.

It is presupposed that communications in the WLAN based on institute ofelectrical and electronics engineers (IEEE) 802.11 standards areperformed within a zone called a basic service set (BSS). The BSS zonehas a somewhat indefinite boundary since it may vary depending onpropagating characteristics of a wireless medium. Such a BSS isbasically divided into two configurations of an independent BSS (IBSS)and an infrastructure BSS. The former indicates a BSS that forms aself-contained network and does not allows access to a distributionsystem (DS), and the latter indicates a BSS that includes one or moreaccess points (AP), a distribution system, etc. and generally employsthe AP in all communications including communication between stations.

The station (STA) having desire to access a wireless network may use twoscanning methods for searching an accessible wireless network (BSS orIBSS), i.e., a candidate AP or the like.

One is passive scanning, which uses a beacon frame transmitted from theAP (or STA). That is, the STA having desire to access a wireless networkperiodically receives the beacon frames from the AP or the like managinga relevant BSS (or IBSS), thereby finding the accessible BSS or IBSS.

The other is active scanning. The STA having desire to access thewireless network first transmits a probe request frame. Then, the STA orAP that receives the probe request frame responds with a probe responseframe.

TV Whitespace includes channels allocated to broadcast TV, which arepermitted to be used by cognitive radio device. TV White Space mayinclude UHF band and VHF band. The spectrum (hereinafter, can be calledas ‘White Space’) not used by a licensed device can be used by anunlicensed device. The frequency band permitted to be used by unlicenseddevice can be differently defined for each country. Generally, thisfrequency band comprises 54-698 MHz (US, Korea), and some of thisfrequency band can't be used for the unlicensed device. Here, ‘licenseddevice’ means a device of the user permitted in this frequency band, andcan be differently called as ‘primary user’, or ‘incumbent user’. Theunlicensed device, which wishes to use the TV White Space (TVWS), shallacquire information for available channel list at its location.

An unlicensed device should provide a protection mechanism for theincumbent user. That is, the unlicensed device should stop using aspecific channel, when an incumbent user, such as wireless microphone,is using that specific channel. For this purpose, spectrum sensingmechanism is required. Spectrum sensing mechanism comprises EnergyDetection scheme, Feature Detection scheme, etc. By using thismechanism, unlicensed device determines that the channel is used by anincumbent user, when the strength of the primary signal is greater thana predetermined level, or when Digital Television (DTV) Preamble isdetected. And, the unlicensed device (station or access point) shalllower its transmit power, when it is detected that the neighboringchannel, next to the channel used by the unlicensed device, is used bythe incumbent user.

On the other hand, in order to efficiently operate the unlicensed deviceon TVWS, more discussion is needed on an enabling mechanism of lettingthe unlicensed device to operate in TVWS, how efficiently the unlicenseddevice finds the network to be connected, how the information for theavailable channel in TVWS is efficiently acquired, efficient format ofthat information, and efficient signaling mechanism to exchange thisinformation, etc.

SUMMARY OF THE INVENTION

A method and apparatus of controlling a transmit power operated in a TVWhite Space transmits in a wireless local area network is provided.

In an aspect, a method of controlling a transmit power of a wirelessdevice operated in a TV White Space in a wireless local area network isprovided. The method includes transmitting, by a first wireless deviceto a second wireless device, a white space map indicating a list ofavailable channels, and transmitting, by the first wireless device tothe second wireless device, an extended power constraint indicating aplurality of transmission channels and a plurality of maximum transmitpowers, wherein the plurality of transmission channels are selectedamong the list of available channels and each of the plurality ofmaximum transmit powers corresponds to a maximum transmit power for eachof the plurality of transmission channels.

The first wireless device and the second wireless device may operate oneach transmission channel at a transmit power below a maximum transmitpower corresponding to each transmission channel of the plurality ofmaximum transmit powers.

The method may further include advertising, by the second wirelessdevice, the extended power constraint indicating the plurality oftransmission channels and the plurality of maximum transmit powers.

The extended power constraint may be included in a beacon frame.

The method may further include receiving, by the first wireless devicefrom the second wireless device, a probe request frame used for arequest for an active scan, and the extended power constraint may beincluded in a probe response frame as a response of the probe requestframe.

In another aspect, a wireless device for controlling a transmit poweroperated in a TV White Space in a wireless local area network isprovided. The wireless device includes a processor configured to acquirea white space map indicating a list of available channels and anextended power constraint indicating a plurality of transmissionchannels and a plurality of maximum transmit powers, and an interfaceunit providing a wireless interface and configured to transmit the whitespace map and the extended power constraint, wherein the processor isconfigured to select the plurality of transmission channels among thelist of available channels, and each of the plurality of maximumtransmit powers corresponds to a maximum transmit power for each of theplurality of transmission channels.

Interference can be mitigated between wireless devices operated in a TVWhite Space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless local area network (WLAN) system to implementthe present invention.

FIG. 2 is a flowchart showing a method of controlling the transmit poweraccording to an exemplary embodiment of the present invention.

FIG. 3 shows an example of using a channel in a TV WS band.

FIG. 4 shows an example of assigning a transmission channel according toan exemplary embodiment of the present invention.

FIG. 5 is a flowchart showing a method for the transmit power constraintaccording to an exemplary embodiment of the present invention.

FIG. 6 is a block diagram showing a format of the beacon frame accordingto an exemplary embodiment of the present invention.

FIG. 7 shows another example of a channel power constraint field.

FIG. 8 is a flowchart showing a method for controlling a transmit poweraccording to another exemplary embodiment of the present invention.

FIG. 9 is a block diagram showing a format of the probe response frameaccording to an exemplary embodiment of the present invention.

FIG. 10 is a block diagram showing an extended power constraintincluding a device type.

FIG. 11 is a block diagram showing examples of extended powerconstraint.

FIG. 12 is a block diagram of a wireless device to implement the presentinvention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless local area network (WLAN) system to implementthe present invention.

Referring to FIG. 1, a WLAN system includes one or more basic serviceset (BSS). The BSS is a group of stations (STA) which can successfullysynchronize and communicate with one another, and does not mean acertain zone.

An infrastructure BSS (BSS1, BSS2) includes one or more non-access point(AP) STAs (non-AP STA1, non-AP STA2, non-AP STA2); APs (AP STA1, APSTA2) providing distribution service; and a distribution system (DS)connecting the plurality of APs (AP STA1, AP STA2). In theinfrastructure BSS, the AP manages the non AP STAs.

On the other hand, an independent BSS (IBSS) is a BSS that operates inan Ad-Hoc mode. Since the IBSS does not include the AP, there is nocentralized management entity that performs centralized management. Thatis, in the IBSS, the non-AP STAs are managed in a distributed manner. Inthe IBSS, all STAs may be provided as mobile STAs and constitute aself-contained network since access to the DS is not allowed.

The STA is a predetermined functional medium having a medium accesscontrol (MAC) and a physical layer interface for a wireless medium,based on institute of electrical and electronics engineers (IEEE) 802.11standards, which broadly includes both the AP and the non-AP STA.

The STA may be called a mobile terminal, a wireless device, a wirelessterminal, a mobile station (MS), a mobile subscriber unit, or the like.

The AP is a functional entity that provides access to the DS via awireless medium for the STA associated with the AP. In theinfrastructure BSS including the AP, communication between the non-APSTAs is basically performed via the AP, but direct communication betweenthe non-AP STAs may be possible if a direct link is set.

The plurality of infrastructure BSSs may be connected to one anotherthrough the distribution system (DS). The plurality of BSSs connectedthrough the DS is called an extended service set (ESS). The STAsincluded in the ESS can communicate with one another, and the non-APSTAs within one ESS can move from one BSS to another BSS whileperforming the communication without disconnection.

The DS is a mechanism that enables one AP to communicate with anotherAP. Through the DS, the AP can transmit a frame for the STAs associatedwith the BS managed by the AP, transmit a frame when one STA moves toanother BSS, or transmit a frame to an external network such as a wirednetwork or the like. The DS is not necessarily a network, but may beachieved without any limitation as long as it can provide predetermineddistribution service based on IEEE 802.11. For example, the DS may be awireless network such as a mesh network, or a physical structureconnecting the APs with one another.

In order for an unlicensed device to operate in TVWS such as a frequencydomain where the unlicensed device is permitted to operate at a giventime in a given geographical area with regard to a licensed device, theunlicensed device should acquire information for available channels inTVWS not used by incumbent users. The most casual approach for this isdefining such that all the unlicensed devices performs sensing whetherthere is a primary signal of the incumbent user on each of the channelsin TVWS. However, it may cost huge overhead, thus another approach canbe using a regulatory database, such as TV band database which includesinformation which of the channels are available for the WLAN operationat specific geographic location.

As stated above, the unlicensed device including STA should provide aprotection mechanism for the incumbent user. That is, if a specificchannel is used by an incumbent user, such as wireless microphone, theunlicensed device should stop using this channel. For that purpose, theunlicensed device can perform spectrum sensing to find whether aspecific channel is used by a primary user. Spectrum sensing mechanism,which can be used, includes Energy Detection scheme, Feature Detectionscheme, etc.

If the unlicensed device finds that the strength of the primary signalis higher than a predetermined level, or if the unlicensed devicedetects the Digital Television (DTV) preamble, the unlicensed device maydetermine that that channel is used by an incumbent user. And, if theunlicensed device determines on a specific channel that the neighboringchannel next to the specific channel is used by the incumbent user, theunlicensed device should lower its transmission power to protect theincumbent user.

FIG. 2 is a flowchart showing a method of controlling the transmit poweraccording to an exemplary embodiment of the present invention.

Referring to FIG. 2, a first STA transmit a white space map to a secondSTA (S210). The white space map includes a list of identified availablechannels and/or corresponding maximum allowed transmission powers foreach available channel. Actual maximum of transmission power level isdecided depending on the channel bandwidth and the maximum allowedtransmission powers per available channel. The first STA may generatethe white space map based on TV channel information from TV bandsdatabase system or its own spectrum sensing.

The first STA transmits channel information and maximum transmit powerinformation to the second STA (S220). The channel information indicatestransmission channels selected among the list of available channels. Themaximum transmit power information indicates the maximum transmit powersfor the transmission channels. The first STA and the STA operate on eachtransmission channel at a transmit power below a maximum transmit powercorresponding to each transmission channel.

Upon receiving the channel information and the maximum transmit powerinformation, the second STA which may be a AP may advertise the channelinformation and the maximum transmit power information to its dependentSTAs.

The first STA and second STA may receive and transmit data frames at thetransmission channels (S230).

The channel information and the maximum transmit power may be varieddepending on the conditions of the frequency band. Thus, the first STAmay update the corresponding information and transmit the updatedinformation to the second STA. To update the channel information and themaximum transmit power information, the first STA may confirm whetherother WLAN systems or a different kind of communication systems is usingthe frequency band, which may be performed by sensing a signaltransmitted from other wireless devices. Also, the first STA may acquireinformation about the state of the usage by accessing a database wherethe channel information or the maximum transmit power information areupdated.

The first STA may send an action frame that contains the channelinformation and the maximum transmit power information. The action framemay be a beacon frame used for a passive scan or a probe response frameas a response to a probe request frame used for an active scan.

If the channel information and the maximum transmit power information isperiodically updated, the updated information may be transmitted asbeing included in a beacon frame periodically transmitted.

A master device may transmit the channel information and the maximumtransmit power information to wireless devices (which is called asdependent devices). The master device may be an AP or a non-AP STA. Themaster device selects transmission channels and their maximum transmitpowers based on a database.

The transmission channels and the maximum transmit powers may bedifferent depending on the types of STA. Thus, the master device maysend the type of service-target STA as well as the channel informationand the maximum transmit power information.

A STA may perform sensing with regard to each channel of the TV WS band,or may request other STA to report a sensing result.

If the STA can access a database containing information related to achannel state of the TV WS band, the STA can acquire the channelinformation without performing spectrum sensing.

The STA grasps the state of each channel through the channelinformation, and shifts to an available channel if a used channel is notavailable anymore as a licensed user appears. As necessary, the STA maypreviously set up a preliminary channel to be used when the used channelis not available anymore.

If a certain channel available for the STA is adjacent to a channelbeing occupied by the licensed user, interference may occur when the STAuses the certain channel. Accordingly, there is a need for a method ofmitigating the interference. To this end, there has been proposed amethod of constraining a transmit power with regard to a channel to beused by the STA.

FIG. 3 shows an example of using a channel in a TV WS band.

In the TV WS, an unlicensed device such as an AP and a STA can generallyuse about 30 channels each of which has a bandwidth of 6 MHz. As aprecondition for using these channels, a certain desired channel has notto be occupied by the licensed user.

Suppose that each of channels 32 a and 32 b being used by the licenseduser has a bandwidth of 6 MHz. In the conventional IEEE 802.11astandard, since the STA supports at least one of 5 MHz, 10 MHz and 20MHz, let the AP and the STA have a standard channel bandwidth of 5 MHz.Thus, the AP and the STA can support a channel bandwidth of 10 MHz or 20MHz by regarding 5 MHz as the standard bandwidth, according to how manyWS channels are successively unoccupied.

Here, a transmission channel refers to a physical wireless resource thatis used by an unlicensed device for transmitting a frame or the likewireless signal in a certain frequency band.

Suppose that the STA can use a central band 31 in the TV WS, thelicensed user is occupying both adjacent channels 32 a and 32 b adjacentto the central band 31, and the central band 31 is a bandwidth of thetransmission channel. The STA has to decrease the transmit power of thetransmission channel 31 when sensing a signal of the licensed user inthe WS channels 32 a and 32 b adjacent to the transmission channel 31being used by the STA. This is to reduce the interference with thelicensed user.

For example, even though allowable maximum transmit power of the STA is100 mW, the maximum transmit power may be limited to 40 through 50 mWwhen the adjacent WS channels 32 a and 32 b are being occupied by thelicensed user. Because of the above, there is no need of directlyassociating a broader bandwidth of a transmission channel with a higherthroughput in consideration of such a transmit power constraint. In somecases, higher transmit power may be more effective instead of using atransmission channel having a relatively narrow bandwidth.

If three WS channels each having the bandwidth of 6 MHz are unoccupiedin the TV WS band, an available band is 18 MHz. The STA can transmit andreceive a frame through the transmission channel having a bandwidth of10 MNz in the foregoing band. However, emptiness of three successive WSchannels means that the adjacent WS channels at both sides are beingoccupied by the licensed user. Therefore, when the frame is transmittedusing the transmission channel having the bandwidth of 10 MHz, thetransmit power has to be constrained to 40 through 50 mW so as toprotect the licensed user occupying the adjacent WS channels.

There may be an environment having a high gain when using low transmitpower in a broad band, but there may be an environment having a low gainwhen using high transmit power in a narrow band. Also, if the transmitpower is lowered, coverage is reduced and a hidden node problem mayarise.

Below, embodiments related to the transmit power constraint forprotecting the licensed user will be proposed. For example, thefollowing exemplary embodiments show that the transmission channels usedby the STAs have bandwidths of 5 MHz, 10 MHz and 20 MHz, and have anormal allowable maximum transmit power of 100 mW and a constrainedmaximum transmit power of 40 mW.

FIG. 4 shows an example of assigning a transmission channel according toan exemplary embodiment of the present invention.

Referring to FIG. 4, suppose that there are seven channels CH1˜CH7 inthe TV WS band, in which middle channels CH2˜CH6 are empty and thelicensed user occupies the channels CH1 and CH7.

Because five channels are empty WS channels, an empty frequency band is30 MHz. With respect to a center frequency f_(c) in the empty frequencyband, the bandwidth available for the STA is at least one of 5 MHz, 10MHz and 20 MHz.

If the STA uses a transmission channel having a bandwidth of 5 MHz, themaximum transmit power of 100 mW can be used since there is no adjacentchannel occupied by the licensed user. Likewise, if the STA uses atransmission channel having a bandwidth of 10 MHz, the maximum transmitpower of 100 mW can be used since there is no adjacent channel occupiedby the licensed user.

On the other hand, if the STA uses a transmission channel having abandwidth of 20 MHz, the maximum transmit power is constrained to 40 mWbecause there is an adjacent WS channel occupied by the licensed user.

FIG. 5 is a flowchart showing a method for the transmit power constraintaccording to an exemplary embodiment of the present invention.

A first STA 510 and a second STA 520 acquire a white space map (S510).The white space map may be acquired based on TV channel information fromTV bands database system or its own spectrum sensing. The second STA 520which acquires the white space map may send the white space map to thefirst STA 510.

An unlicensed user having no priority for using the TV WS band confirmswhether the licensed user having the priority exists or not throughperiodic channel sensing, and immediately stops using the currentlyoccupied channel if there exists the licensed user.

The first STA 510 receives a beacon frame including an extended powerconstraint from the second STA 520 (S520). The beacon frame is amanagement frame that includes network information of the infrastructureBSS configured by the second STA 520. The second STA may be a AP.

The first STA 510 and second STA 520 may receive and transmit dataframes based on the extended power constraint (S530).

The extended power constraint indicates transmission channels andmaximum transmit powers. The transmission channels are selected amongthe list of available channels in the white space map. The first STA 510can acquire information about WS channels and their power constraints byreceiving the beacon frame, and thus determine the maximum allowabletransmit power for each transmission channel.

FIG. 6 is a block diagram showing a format of the beacon frame accordingto an exemplary embodiment of the present invention.

Referring to FIG. 6, a beacon frame includes a media access control(MAC) header 50, a frame body 60, and a frame check sequence (FCS) 70.

The frame body 60 includes a timestamp field 61, a beacon interval field62, a capability field 63, and an extended power constraint field 600.

The timestamp field 61 includes information used for timesynchronization. The beacon interval field 62 includes information aboutan interval at which the beacon frame is transmitted. The capabilityfield 63 includes information about a condition required forcommunication between a AP and a STA in the BSS.

The extended power constraint field 600 includes an extended powerconstraint including information about constraining the transmit powerused for each transmission channel. The extended power constraint field600 may include an element identifier (ID) field 610, a length field620, and one or more channel power constraint fields 631. In thisexemplary embodiment, two channel power constraint fields are shown, butnot limited thereto.

The element ID field 610 indicates that a corresponding informationelement is the extended power constraint. The length field 620 indicatesthe length of the extended power constraint field 600.

A channel power constraint field 631 includes a channel bandwidthsubfield 631 a indicating a channel bandwidth of a transmission channel,and a maximum transmit power subfield 631 b indicating the maximumtransmit power of the transmission channel.

The transmission channel bandwidth subfield 631 a denotes a channelbandwidth available for the STA. The maximum transmit power subfield 631b denotes the maximum transmit power allowable in the channel bandwidthindicated by the transmission channel bandwidth subfield 631 a.

In the example of FIG. 4, the maximum transmit power of 100 mW may begiven to the transmission channel having a bandwidth of 5 MHz, themaximum transmit power of 100 mW may be given to the transmissionchannel having a bandwidth of 10 MHz, and the maximum transmit power of40 mW may be given to the transmission channel having a bandwidth of 20MHz. Thus, the extended power constraint field 600 includes threechannel power constraint fields.

On the basis of the extended power constraint, a STA may determine atransmit power of a transmission channel within a range of the maximumtransmit power constraint.

FIG. 7 shows another example of a channel power constraint field.

A channel power constraint field 731 includes a channel number subfield731 a and a maximum transmit power subfield 731 b.

The channel number subfield 731 a indicates a channel number used toidentify a transmission channel. The maximum transmit power subfield 731b indicates a maximum transmit power allowable to the transmissionchannel.

In the example of FIG. 4, the channel number subfield 731 a may indicateone among the channels CH2 through CH6. If the WS channel numbersubfield 731 a indicates one among the channels CH3 through CH5, themaximum transmit power may be given as 100 mW. If the WS channel numbersubfield 731 a indicates one between the channels CH2 and CH6, themaximum transmit power may be given as 40 mW.

FIG. 8 is a flowchart showing a method for controlling a transmit poweraccording to another exemplary embodiment of the present invention.

A first STA 810 and a second STA 820 acquire a white space map (S810).The white space map may be acquired based on TV channel information fromTV bands database system or its own spectrum sensing. The second STA 820which acquires the white space map may send the white space map to thefirst STA 810.

The first STA 810 transmits a probe request frame to the second STA 820to initiate active scanning (S820).

As a response to the probe request frame, the second STA 820 sends aprobe response frame including an extended power constraint to the firstSTA810 (S830).

The first STA 810 and second STA 820 may receive and transmit dataframes based on the extended power constraint (S840).

FIG. 9 is a block diagram showing a format of the probe response frameaccording to an exemplary embodiment of the present invention.

Referring to FIG. 9, a probe response frame includes a MAC header 80, aframe body 90 and a FCS 100.

The frame body 90 includes a timestamp field 91, a beacon interval field92, a capability field 93, and an extended power constraint field 600.These fields are the same as the timestamp field 61, the beacon intervalfield 62, the capability field 63, and the extended power constraintfield 600 shown in the embodiment of FIG. 6.

In the meantime, the available channel and the maximum allowabletransmit power may be different depending on the types of STA. Forexample, the STA corresponding to a fixed device cannot use the WSchannel adjacent to the WS channel being occupied by a licensed user. Onthe other hand, the STA corresponding to a personal/portable device canuse the adjacent WS channel under the condition that the maximumtransmit power is limited to a certain range, e.g., from 100 mW to 40mW.

Accordingly, the STA can need to send the type of its own service-targetSTA.

FIG. 10 is a block diagram showing an extended power constraintincluding a device type.

Referring to FIG. 10, an extended power constraint field 1000 includesan element ID field 1010, a length field 1020, a device type field 1030,and one or more channel power constraint fields 1040. The element IDfield 1010 and the length field 1020 are the same as the fields 610 and620 shown in the embodiment of FIG. 6.

The device type field 1030 indicates a type of a STA to be serviced bythe AP. If there are two types of STA such as a fixed device and apersonal/portable device, it is possible to distinguish the type ofcorresponding STA on the basis of a bit value that the device type field1030 has. The device type field 1030 may indicate each type of STA, or aset of certain-typed STA. The size of the device type field 1010 may bevaried depending on the types of STA.

The channel power constraint field 1041 includes a channel numbersub-field 1041 a and a maximum transmit power sub-field 1041 b.

The extended power constraint field 1000 may be transmitted as beingincluded in a beacon frame, a probe response frame, or other managementframes.

The STA can be informed of whether the included information is for whattype of device, by acquiring the extended power constraint field 1000.Also, the STA can be informed of the maximum transmit power allowablefor the corresponding channel.

FIG. 11 is a block diagram showing examples of extended powerconstraint. Here, it is assumed that a WS channel #1 and a WS channel #3are adjacent to the WS channel occupied by a licensed user. In thiscase, a STA corresponding to a fixed device can use only the WS channel#2, and the STA corresponding to a personal/portable device can use atleast one of the WS channels #1, #2 and #3.

As shown in a subfigure (a) of FIG. 11, a channel power constraintfields about the WS channels available to the types of STA may beincluded in a extended power constraint fields, respectively. If adevice type field 1111 indicates a STA corresponding to a fixed device,an extended power constraint field 1110 includes a channel powerconstraint field 1112 about the WS channel #2. If a device type field1121 indicates a STA corresponding to a personal/portable device, anextended power constraint information field 1120 includes channel powerconstraint fields 1122, 1123, 1124.

As shown in a subfigure (b) of FIG. 11, a channel power constraint fieldabout the WS channel available in common to the types of STA may beincluded in one extended power constraint information field, and thechannel power constraint fields about the WS channel available to onlythe respective types of STA may be included in different extended powerconstraint information fields, respectively. If a device type field 1131indicates a STA corresponding to a fixed device and a personal/portabledevice, an extended power constraint information field 1130 includes achannel power constraint field 1132 about the WS channel #2. If a devicetype field 1141 indicates a STA corresponding to a personal/portabledevice, an extended power constraint information field 1140 includeschannel power constraint fields 1142 and 1143 about the WS channels #1and #3.

FIG. 12 is a block diagram of a wireless device to implement the presentinvention. The wireless device 1200 may be a part of a STA or an AP andmay be a first STA or a second STA shown in embodiments of FIGS. 2, 5and 8. The wireless device 1200 may operate in a TV WS.

The wireless device 1200 includes a processor 1210, a memory 1220 and aninterface unit 1230.

The processor 1210 implements functions of the first STA or the secondSTA shown in embodiments of FIGS. 2, 5 and 8. The processor 1210 mayacquire a white space map and generate an extended power constraint. Thememory 1220 is operatively coupled with the processor 1210 and storesvarious information. The interface unit 1230 is operatively coupled withthe processor 1210 and provides a wireless interface with other wirelessdevice. The white space map and the extended power constraint may betransmitted via the interface unit 1230.

The processor may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememory may include read-only memory (ROM), random access memory (RAM),flash memory, memory card, storage medium and/or other storage device.When the embodiments are implemented in software, the techniquesdescribed herein can be implemented with modules (e.g., procedures,functions, and so on) that perform the functions described herein. Themodules can be stored in memory and executed by processor. The memorycan be implemented within the processor or external to the processor inwhich case those can be communicatively coupled to the processor viavarious means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1. A method of controlling a transmit power of a wireless deviceoperated in a TV White Space in a wireless local area network,comprising: transmitting, by a first wireless device to a secondwireless device, a white space map indicating a list of availablechannels; and transmitting, by the first wireless device to the secondwireless device, an extended power constraint indicating a plurality oftransmission channels and a plurality of maximum transmit powers,wherein the plurality of transmission channels are selected among thelist of available channels and each of the plurality of maximum transmitpowers corresponds to a maximum transmit power for each of the pluralityof transmission channels.
 2. The method of claim 1, wherein the firstwireless device and the second wireless device operate on eachtransmission channel at a transmit power below a maximum transmit powercorresponding to each transmission channel of the plurality of maximumtransmit powers.
 3. The method of claim 1, further comprising:advertising, by the second wireless device, the extended powerconstraint indicating the plurality of transmission channels and theplurality of maximum transmit powers.
 4. The method of claim 1, whereinthe extended power constraint is included in a beacon frame.
 5. Themethod of claim 1, further comprising: receiving, by the first wirelessdevice from the second wireless device, a probe request frame used for arequest for an active scan, and wherein the extended power constraint isincluded in a probe response frame as a response of the probe requestframe.
 6. The method of claim 1, wherein the extended power constraintincludes information to identify the plurality of transmission channels.7. The method of claim 6, wherein each of the plurality of transmissionchannels is identified by a bandwidth of each transmission channel and achannel number of each transmission channel.
 8. The method of claim 1,wherein the white space map includes maximum allowed transmit powers foreach available channel.
 9. The method of claim 1, wherein the secondwireless device is an access point (AP).
 10. A wireless device forcontrolling a transmit power operated in a TV White Space in a wirelesslocal area network, comprising: a processor configured to acquire awhite space map indicating a list of available channels and an extendedpower constraint indicating a plurality of transmission channels and aplurality of maximum transmit powers; and an interface unit providing awireless interface and configured to transmit the white space map andthe extended power constraint, wherein the processor is configured toselect the plurality of transmission channels among the list ofavailable channels, and each of the plurality of maximum transmit powerscorresponds to a maximum transmit power for each of the plurality oftransmission channels.
 11. The wireless device of claim 10, wherein theinterface unit is configured to operate on each transmission channel ata transmit power below a maximum transmit power corresponding to eachtransmission channel of the plurality of maximum transmit powers. 12.The wireless device of claim 10, wherein the extended power constraintis included in a beacon frame.
 13. The wireless device of claim 10,wherein the extended power constraint is included in a probe responseframe as a response of a probe request frame.
 14. The wireless device ofclaim 10, wherein the extended power constraint includes information toidentify the plurality of transmission channels.